The invention relates to a configuration for triggering a restraint device in a motor vehicle having a sensor for accident detection. The sensor outputs an impact signal in the event of an impact of the vehicle. A control device, which is connected downstream of the sensor, generates a control signal in response to the impact signal supplied by the sensor. The configuration further has a firing device, which is disposed spatially separately from the control device and is connected to the latter via a line, and a firing element for the restraint device, which is electrically coupled to the firing device.
A configuration of this type has a DC signal for operating the firing device and the DC signal is coupled onto a line and an AC signal containing messages for firing triggering is additively superposed on the DC signal. The composite signal is then transmitted from an evaluation device to the firing device and appropriately evaluated there. Although the problem of undesired firing caused by interference pulses which arises in the case of direct-current firing is counteracted in this known configuration, the requisite outlay is very high.
It is accordingly an object of the invention to provide a configuration for triggering a restraint device in a motor vehicle which overcomes the above-mentioned disadvantages of the prior art methods of this general type, in which interference immunity is achieved with a lower outlay.
With the foregoing and other objects in view there is provided, in accordance with the invention, a configuration for triggering a restraint device in a motor vehicle. The configuration contains a sensor for accident detection, the sensor outputting an impact signal in an event of an impact on the vehicle. A control device is connected downstream of the sensor and generates a control signal in response to the impact signal supplied by the sensor. The control signal is composed of a first current in a first direction and a subsequent second current in second direction opposite the first direction. A firing element for firing the restraint device and a firing device disposed spatially separate from the control device and is connected to the control device through the line and also is electrically coupled to the firing element. The firing device has an integration device for integrating the first current and an enable device connected downstream of the integration device and serving for enabling firing of the firing element. The firing of the firing element is effected by the second current when a limit value of an integral of the first current has been reached.
It is an advantage of the invention that the required logic complexity for remote-controlled firing (remote firing system) can be considerably reduced, thereby reducing costs and space requirement. In particular, there is no need for any components in the wiring harness, so that all components can be integrated in the firing pellet (e.g. semiconductor firing pellet).
This is achieved in particular by the fact that the configuration is provided which permits firing only after an activation phase (preferably heating phase). In this case, the current flow for activation is opposite to the current direction in the case of firing.
In detail, the configuration according to the invention contains, in particular, the sensor for accident detection, which generates the impact signal, and the control device, which is connected downstream of the sensor and generates the control signal in response to the impact signal supplied by the sensor. The firing device is disposed spatially separate from the control device and is connected to the latter via a line, the firing element for the restraint device is electrically coupled to the firing device. The control signal generated by the control device is composed, according to the invention, of a first current in one direction and a subsequent second current in the opposite direction. The firing device contains the integration device for integrating the first current, and also the enable device, which is connected downstream of the integration device and serves for enabling firing of the firing element. The firing of the firing element is effected by the second current when or after a limit value of the integral of the first current has been reached.
The integration is preferably effected thermally by a heating element and a mass thermally coupled thereto. In this case, the enable device has a temperature-sensitive switch, which is thermally coupled to the mass and switches through to the firing element when a limit value temperature of the mass has been reached. The xe2x80x9cthermal integrationxe2x80x9d has the advantage that it requires little outlay, on the one hand, and affords a high interference immunity, on the other hand.
The temperature-sensitive switch provided may be a transistor, whose controlled path is connected in series with the firing element and whose control terminal is coupled to the control signal generated by the control device, in such a way that the transistor always turns off in the case of the first current and turns on in the case of the second current only when the temperature at the transistor is greater than or equal to the limit value temperature. In this case, the temperature dependence of transistors can advantageously be utilized in order, in conjunction with a low outlay and space requirement, to realize a temperature-dependent switch which, moreover, can also distinguish current directions given appropriate circuitry.
By way of example, the transistor provided is a bipolar transistor or a MOS field-effect transistor, whose base/gate is connected to a tap of a voltage divider fed with the control signal, whose emitter/source is connected to one terminal of the firing element, and whose collector/drain is connected to one terminal of the voltage divider, the other terminal of the voltage divider being connected up to the other terminal of the firing element. Bipolar transistors are very simple to produce and are distinguished by high robustness with respect to external influences (for example momentary electrostatic discharges of high voltage). MOS field-effect transistors advantageously require only a small driving current and, therefore, no costly driver circuits for driving.
In order to save space and reduce additional outlay, the mass may in this case be formed from the temperature-sensitive switch (for example semiconductor body of the transistor) and/or the heating element (for example semiconductor body of a diode serving as the heating element).
The heating element is preferably configured in such a way that although the heating element can be heated by the first current, it cannot be heated by the second current, and that the first current is pulsed, with the heating element only being able to be heated by alternating currents. This increases the interference immunity of the entire configuration.
Contributions to further increasing the interference immunity are made, moreover, by the measures that a low-pass filter is connected between the control device and the firing device, and/or that the first and/or second current are coded, there being connected upstream of the temperature-sensitive switch a decoding device for additional firing enabling.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a configuration for triggering a restraint device in a motor vehicle, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.